ANALYSIS OF A PICTOU COAL SEAM—GILPIN. 45 
streams to cut through coal beds, they carried only the finest 
sediments. An illustration of this recently came under my 
notice in the Cumberland district, where a brook of the carboni- 
ferous period had eroded the coal down to and partly through 
the underclay, the “want” being filled with a fine laminated 
gray shale. This is also interesting, for from the abrupt passage 
from coal to shale it is apparent that even at that early date in 
the history of the future coal bed it must have acquired a certain 
amount of coherence, enough to form the banks of even a slug- 
gish stream. 
. There is another interesting point in connection with coal 
seams which I have not yet seen referred to in any books on 
this subject. That is the influence of the water and land sur- 
rounding the coal producing district upon the purity and homo- 
geneity of the resulting coal bed. It is frequently found by the 
miner that, as he follows the seam, it changes its character. At 
first he was proud of the absence of “bands and balls” and of 
the facility with which he could supply pure coal. Gradually he 
finds that the bands of shale grow larger with ominous persist- 
ence. At last he awakens to the fact that his coal is getting 
_“boney ;” finally it proves unmarketable, and he turns his levels 
in another direction. 
Sometimes trial-pits and bore-holes in advance prove that 
the coal has become a mere mass of carbonaceous shale, or that 
the seam has ceased. These changes may frequently be explained 
by the proximity of the vegetation to an arm of the sea or to a 
river, so that the deposition of mud from floods, ete., at first 
slight, becomes greater, both in the form of bands, and of a general 
addition of clayey and silicious matter. Finally a point is 
reached where the conditions of coal deposition ceased. In some 
cases the proximity of land covered by sand, which was carried 
by prevailing winds upon the accumulating vegetation, may 
explain the presence of an excessive amount of ash in seams not 
holding bands of shale. It may also have been possible that 
_ both these causes united to the deterioration of seams of coal. 
This would show that some of the beds were formed in what 
might be termed broad shallow basins, in the centre of which is 
